Hmmmmmmmm -scratches chin-
Average weight of human, 80 kg.
Let's assume each passenger will need 120 kg of support (renewable food, medicine, etc).
Let's also assume we have 100 humans to start a small colony.

We now have a 20,000 kg spacecraft, which is pretty much the absolute minimum. The kinetic energy of such a ship going at 0.95 c is gonna be ....
KE = m c^2 [(1-v^2/c^2)^(-1/2) - 1] ≈ 2.2 m c^2
≈ 4 * 10^21 Joules

For reference, the *world* energy production in 2008 was 4.7*10^20 Joules.

So it would take the total output of the world's electricity 10 years to accelerate this craft. Double that, actually, since the propellant coming out the back would have to have the same energy going the other way.

Utilizing the gravitational fields of stars starting with our very own sun to accerate and decelerate could reduce energy consumption considerably. Imaging the speed one could obtain over the severl months of droping in for close pass of our sun from a distance out past Pluto.